In tuber crops, such as the potato, the storage proteins that accumulate in the plant cell vacuole support the growth of new plants. It is these same storage proteins and carbohydrates that give these tubers nutritional value. The storage proteins, however, may serve other functions as well. For example, in the potato, the protein patatin shows phospholipase A2 activity and inhibits the growth of worm larvae. Like the potato, the oca (Oxalis tuberosa) originates in the highland areas of the Andes, tolerates cool climates and very poor soils, and possesses tubers of equivalent nutritive value.

Now Flores et al. have shown that a storage protein from oca also does double duty. The protein ocatin accounts for up to 60% of the soluble protein in oca tubers and also turns out to have antipathogen activities. The protein sequence of ocatin resembles those of another group of proteins that are expressed intracellularly after pathogen attack. Thus ocatin provides both a nutritional store and potentially provides natural protection from phytopathogenic bacteria and fungi.—PJH